The present invention relates generally to the field of character recognition and more specifically to mechanisms for recognizing cursive writing. It is important to distinguish ordinary cursive writing to which the present invention relates from the more restrictive forms of hand printing which represent the current state of the art of automatic character recognition. In this later instance there are a number of products on the market including the IBM 1287 Optical Scanner, as well as the RAND and SDC tablet programs, which recognize individual hand printed symbols which must be separate and disconnected from each other. In addition these symbols usually must be constrained insofar as shape and size is concerned.
A major problem faced in the analysis of cursive script is the segmentation of the words automatically into characters suitable for a recognition mechanism based on characters to operate upon. Although there have been attempts to perform "whole word recognition," such systems have not worked at all well and are of theoretical interest only.
Although such systems are workable they have a rather severely limited utility as they are not able to process what would be classified as normal cursive writing written at a person's normal writing speed.
U.S. Pat. No. 3,111,646 dated Nov. 19, 1963 of L.D. Harmon discloses a method and apparatus for reading cursive script. In this patent the inventor discloses a system for achieving the analysis of cursive script writing. The system disclosed in this patent has a number of defects, foremost being the fact that the segmentation algorithm being unduly restrictive, requires the writing to be well-proportioned. Harmon determines various zones by taking the overall height of an entire line, from the bases of the descenders to the peaks of the ascenders, and divides the height into four parts for use in the recognition system. This requires that the input be very well-proportioned and that the writing not slope or deviate from the baseline. It has been found in practice that the heights of ascenders and descenders are a matter of personal sytle and are highly variable. The absolute of an ascender or descender is not of great importance to humans. What is important is the fact that such an event has taken place.
The above referenced Harmon patent contains a segmentation algorithm that is entirely retrospective. That is, an entire line of script is taken into storage registers, and the segmentation points are determined by first determining the average letter width, based principally on the number of zero axis crossings. This has a number of drawbacks in addition to those specifically mentioned in the patent. First, it requires that the input be very well-proportioned, i.e., that the writer maintain substantially the same letter width throughout. Secondly, it is not sequential. For a practical system, it is desirable for segmentation and recognition to be done in "real time". That is the system should display its results as soon as possible after the character is formed.
This system is intended to replace conventional dictation. It should given transcription of "rough draft" quality.
As is well known one of the more common forms of representing alphanumeric data is cursive script. In order to achieve machine recognition of the connected characters which form cursive script words it is necessary that the words be segmented into their individual letter components. Segmentation in itself is an extremely difficult problem in the case of connected written script, in view of the extraordinary numbers of variations handwritten material may take. The form of the ligature depends on the two characters being joined, the overall context, and such general factors as fatigue and the physical conditions under which the writing is done, i.e., sitting, standing, etc.
As stated previously U.S. Pat. No. 3,111,646 of Harmon attacks the segmentation problem in a rather imprecise manner, and at best can only approximate segmentation. Thus as a writer's letter width varies greatly or for some reason certain letters do not have zero crossings the segmentation will in all probablity be wrong. It is apparent from the previous discussion that some more precise method for automatically segmenting the individual characters in cursive script handwriting must be provided for such systems to be at all practical.